JPH0357285A - Semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To improve an optical transmission characteristic by integrating a semiconductor laser section, a light absorption modulation section, and a phase modulator section on the same substrate. CONSTITUTION:On the same substrate are integrated a semiconductor laser section LD which has a laser light generation active layer, and a drive current electrode PS1, a light absorption type modulation section MD-EA, which has a light absorption layer adjoining this active layer, and a modulation voltage electrode PS2, a phase modulator MD-P, which is provided with a phase modulation layer adjoining this light absorption layer, and a modulation current electrode PS3. When an attempt is made to carry out phase modulation in reverse phase mode between the MD-P section and phase modulation where laser light is subjected to phase modulation the section MD-EA, cancellation is produced so that wavelength chapping may be zero or work in reverse direction, thereby upgrading the optical transmission characteristic.

Description

[Detailed Description of the Invention] [Summary] Distributed feedback (d
distributed feedback: DF
B) Regarding a semiconductor light emitting device that integrates a type semiconductor laser and a semiconductor modulator, in a semiconductor light emitting device that integrates a DFB type semiconductor laser and a semiconductor modulator, wavelength chirping that occurs during modulation is further reduced, The purpose is to enable high-quality ultra-high-speed optical transmission, and the semiconductor laser part has an active layer for generating laser light and an electrode for flowing a driving current, and a structure that allows the laser light to enter. a light absorption modulator portion having a light absorption layer connected to the active layer and having an electrode through which a modulation current flows for light absorption modulation of the laser beam, the light absorption modulation and the light absorption type; It has a phase modulation layer that is continuous with the light absorption layer so that the laser light that has undergone phase modulation accompanying modulation can be incident, and that is phase modulated in an opposite phase to the phase modulation that the laser light is undergoing. A phase modulator portion having an electrode for passing a modulation current for the purpose of the invention is integrated on the same substrate, or the semiconductor laser portion, the phase modulator portion, and the light absorption type modulator portion are connected in series in that order. The aim is to ensure that these components are integrated on the same substrate.

[Industrial Application Field] The present invention is directed to distributed feedback, which is popular as a light source for ultrahigh-speed optical transmission systems.
The present invention relates to a semiconductor light emitting device that integrates a DFB type semiconductor laser and a semiconductor modulator.

Currently, optical transmission systems are increasing their capacity.
To achieve this, DFB is used as a light source.
It is essential to improve the high-speed response of semiconductor lasers.

[Conventional technology]

For example, a DFB type semiconductor laser with a speed of 10 [gigabits/second]
When modulating at extremely high speeds, high-quality optical transmission cannot be expected unless relaxation oscillations, which cause chirping in the oscillation wavelength, are suppressed.

Therefore, attempts have been made to use an external modulation method that causes significantly less relaxation oscillation than a method that directly modulates a DFB type semiconductor laser.

FIG. 5 is a cross-sectional side view of essential parts for explaining a semiconductor light emitting device that integrates a DFB type semiconductor laser and a semiconductor modulator developed by the present inventor.

In the figure, 1 is an n-type rnP substrate, 2 is a diffraction grating, 3 is a GarnAsP waveguide layer, 4 is an InP etch stop layer,
5 is GaInAsP active layer, 6 is GalnAsP
7 is an InP clad layer, 8 is a high resistance isolation region, 9 is a p + type GalnAsp layer, IOA and I
OB is a p-side electrode, 11 is an n-side electrode, 12 is an anti-reflection coating film made of SiN, LD is a semiconductor laser part, M
D indicates the semiconductor modulator section. The high-resistance isolation region 8 plays a role of insulating the laser portion LD and the modulator portion MD, and the active layer 5 has a compositional strength of λPL=1.54 Cμm when the photonescence wavelength is set to ξ, and the absorption The composition of layer 6 is λP in terms of photoluminescence wavelength.
L=1.42 Cμm], and furthermore, the thickness of the active layer 5 and the light absorption layer 6 is approximately o. iscμm].

In this semiconductor light emitting device, when a current is passed between the electrode 10A and the electrode 11, oscillation occurs in the laser portion LD, and light with a wavelength of 1.55 Cμm generated in the active layer 5 is transmitted to the modulator portion MD. The wave is guided to the absorption layer 6.

Therefore, when no reverse voltage is applied between the electrodes 10B and 11, the energy band gap of the absorbed N6 is larger than that of the active layer 5, so 1.5
Even if a laser beam of 4 C μm is incident, it is emitted as it is through the non-reflection coating film 12 without generating electrons or genuine tags. However, when a reverse voltage is applied between the electrode 10B and the electrode l1, the light absorption layer 6
The energy band gap of becomes small, and when the laser beam is incident there, electrons and holes are generated, so-called
Since it becomes a photocurrent and is consumed, no laser light is emitted.

As is clear from the above, the emitted light can be turned on or off depending on whether or not a current is passed between the electrode 10B and the electrode 11.
It is turned off and modulation is performed.

[Problem to be solved by the invention]

In the semiconductor light emitting device described with reference to FIG. 5, the modulation signal is, of course, applied only to the modulator portion MD. In this case, the emitted light is subjected to phase modulation, resulting in wavelength chirping. Although the wavelength chirving is significantly lower than that of the DFB semiconductor laser using the direct modulation method, it is not zero.
It cannot be ignored.

FIG. 6 is a diagram for explaining the state of modulation in the semiconductor light emitting device shown in FIG. 5, and FIG. 7 is a diagram for explaining the occurrence of wavelength chirping. be.

In Figure 6, the vertical axis represents the optical output, and the horizontal axis represents time. In Figure 7, the vertical axis represents the output wavelength, and the horizontal axis represents time. It has been taken.

As is clear from the figure, wavelength chirving appears following the modulation of light; the wavelength increases when the optical output falls, and decreases when the optical output rises.
The fluctuation value W, is approximately 0. It is about 5 [persons], and reaches about 0.8 [persons] during multi-giga bif} modulation.

The present invention aims to further reduce wavelength chirping that occurs during modulation in a semiconductor light emitting device that integrates a DFB type semiconductor laser and a semiconductor modulator, thereby enabling high-quality ultrahigh-speed optical transmission.

[Means to solve the problem]

As is clear from the explanation of Figures 5 to 7, wavelength chirping chirps toward longer wavelengths when the optical output falls, and chirps toward shorter wavelengths when the optical output rises. It's chirping.

Therefore, if measures are taken to counteract this phenomenon, the problem should be resolved.

1 to 3 are Bronoch diagrams of essential parts of a semiconductor light emitting device for explaining the principle of the present invention.

In each figure, LD is a semiconductor laser part, MDEA is a light absorption modulator part, MD-P is a phase modulator part, and Psi
, PS2 is a power supply for light absorption type modulation, and PS3 is a power supply for phase modulation. In addition, the modulation voltage from the light absorption type modulation power supply PS2 and the phase modulation power supply PS
The phase is opposite to that of the modulation voltage from 3, and it is preferable to use a DFB type semiconductor laser portion LD.

As is clear from the figure, in the present invention, the same parts as the semiconductor light emitting device explained with reference to FIG. In addition to the portion consisting of the portion MD-EA, a phase modulator portion MD-P is provided.

As shown in FIG. 1, this phase modulator part MD-P includes a semiconductor laser part LD and a light absorption type modulator part MD-
EA, or as shown in FIG. 2, the semiconductor laser section LD and the light absorption modulator section MD-EA are combined after being combined, or as shown in FIG. , the configuration shown in FIG. 1 and the configuration shown in FIG. 2 may be combined, or any other configuration may be adopted.

The reason why a light absorption modulator and a phase modulator are used together as a modulator is that, as explained in FIGS. 5 to 7, when only a light absorption modulator is used, the light absorption When transmitting light, the output wavelength shifts to the long wavelength side, and when transmitting light, the output wavelength shifts to the short wavelength side, resulting in phase modulation. Therefore, the refractive index change in the phase modulator is Phase modulation of the output light is achieved by shifting the output wavelength to a phase opposite to that of the absorption modulator so that the wavelength chirving can be moved to zero or in the opposite direction. This is to enable arbitrary control.

As described above, in the semiconductor light emitting device according to the present invention, an active layer (for example, I
A semiconductor laser portion (e.g., semiconductor laser portion LD) having nGaAsP activity 1i5) and having an electrode (e.g., electrode 13A) through which a driving current flows; A light absorption type transformer portion (for example, a light absorption modulation type) having an absorption layer (for example, a GaTnAsP light absorption layer 6) and an electrode (for example, an electrode 13B) through which a modulation current flows for light absorption type modulation of the laser beam. a phase modulation layer (e.g. GarnAsP phase modulation layer 6') and an electrode (for example, electrode 13C) through which a modulation current is passed to perform phase modulation with an opposite phase to the phase modulation that the laser beam is receiving.
) having a phase modulator section (e.g. phase modulator section MD
-P) on the same substrate (for example, an n-type 1nP substrate), or a semiconductor laser portion having an active layer for generating laser light and an electrode for passing a driving current, and It has a phase modulation layer connected to the active layer so that the laser beam can be incident thereon, and the phase modulation layer is phase-modulated in an opposite phase to the phase modulation that would be received when the laser beam is subjected to optical absorption modulation. a phase modulator portion having an electrode through which a modulation current flows for the purpose of the phase modulation, and a light absorption layer connected to the phase modulation layer so that the phase modulated laser light can be incident thereon; A light absorption modulator portion having an electrode through which a modulation current for light absorption modulation is passed is integrated on the same substrate.

[Effect]

By adopting the above-mentioned means, phase modulation is performed in conjunction with optical absorption modulation of the laser beam in the optical absorption modulator section, resulting in wavelength chirving on the long wavelength side or wavelength chirping on the short wavelength side. Even if chirving occurs, its phase modulation can be achieved by passing the laser light through a phase modulator section in advance, or by
The laser beam that has undergone phase modulation is passed through a phase modulator section, where it is canceled out by performing phase modulation with an opposite phase to the phase modulation, and the wavelength chirping is reduced to zero or even in the opposite direction. It is possible to improve the optical transmission characteristics by making it move.

〔Example〕

FIG. 4 shows a cutaway side view of essential parts of one embodiment of the present invention, and FIG.
The same symbols as those used in FIGS. 7 to 7 indicate the same parts or have the same meanings.

In the figure, 6' is a GalnAsP phase modulation layer, 13A
13B is the electrode of the semiconductor laser portion LD, 13B is the electrode of the light absorption layer type modulator portion MD-EA, and 13C is the phase modulator portion M.
DP electrodes, l4 is a driving power source, 15 is a light absorption type modulation power source, and l6 is a phase modulation power source.

As is clear from the drawings, this embodiment is similar to the semiconductor laser portion LD and light absorption modulator portion MD in the semiconductor light emitting device according to the prior art described with reference to FIGS. 5 to 7.
(that is, MD-EA in this embodiment) has a phase modulator section M
It is prepared by adding D-P, and the active layer 5
, the light absorption layer N6 and the phase modulation layer 6' are made of GalnAsP, and the composition thereof is, for example, 1.55C in terms of wavelength sensitivity.
μm), 1.4Cμm], and 1.3Cμm].

Note that if the wavelength sensitivity of the phase shift #[i6' is set to about 1.3 [μm], it will remain transparent even during deep reverse bias operation.

In this embodiment, when a modulation current is caused to flow from the light absorption type modulation power source 15 to the electrode 13B, the refractive index is decreased from the phase modulation power source 16 to the electrode 13C, and the wavelength is shifted to the shorter wavelength side. In addition, when cutting off the modulation current flowing from the light absorption modulation power supply 15 to the electrode 13B, the refractive index is increased from the phase modulation power supply a 16 to the electrode 13C to change the wavelength to a longer wavelength. A current is applied to shift to the side. Therefore, the laser light generated by the active N5 is incident on the light absorption layer 6, where it undergoes light absorption type modulation, and accompanying the modulation, phase modulation in which the wavelength shifts to the longer wavelength side and the shorter wavelength side is generated. After receiving the light, it enters the phase modulation 16', and when passing through there, it receives modulation with an opposite phase that is synchronized with the phase modulation that occurred accompanying the light absorption type modulation, so that the wavelength chirping becomes approximately zero. The laser beam is emitted.

Active layer 5, light absorption layer 6, phase modulation layer 6 in this example
' or by applying conventional techniques. That is, [1. Ga rnAs on the lInP ethoching stop layer 4
P゛The active layer 5 is lengthened to a certain extent.

(The 21 Ga T n A s P active layer 5 is patterned to leave only the portion corresponding to the semiconductor laser portion LD and remove the rest.

(31 G a I n A s P The light absorption layer 6 is lengthened and exposed to light absorption type modulator portion M.
Leave only the part corresponding to DEA and remove the rest.

(41 Grow the GalnAsP phase modulation layer 6',
It is patterned to leave only the part corresponding to the phase modulator part MDP and remove the rest.

As described above, the active layer 5, the light absorption layer 6, the phase modulation N6
'Each composition has a wavelength sensitivity λ, L of 1.55 C
μm), 1.4 (μm), 1.3 Cpm], and the lengths of each of the semiconductor laser portion LD, light absorption modulator portion MD-EA, and phase modulator portion MD-P are 300 (μm). ), 200 [μrr+), 40
It was set to 0 (μm).

〔Effect of the invention〕

In the semiconductor light emitting device according to the present invention, there is provided a semiconductor laser portion having an active layer for generating laser light and an electrode through which a driving current flows; a light absorption modulator portion having a light absorption layer connected to the laser beam and an electrode through which a modulation current flows for light absorption modulation of the laser beam; a phase modulation layer that is continuous with the light absorption layer so that the laser beam that has undergone phase modulation can be incident thereon, and that modulates the phase with an opposite phase to the phase modulation that the laser beam is undergoing; A phase modulator section having an electrode for applying a voltage is integrated on the same substrate, or the semiconductor laser section, the phase modulator section, and the light absorption modulator section are connected in series in that order and are integrated on the same substrate. Integrated on a substrate.

By employing the above structure, phase modulation is performed along with optical absorption modulation of the laser beam in the optical absorption modulator section, resulting in wavelength chirping on the long wavelength side or wavelength chirping on the short wavelength side. Even if wavelength chirping occurs, the phase modulation can be achieved by passing the laser light through a phase modulator section in advance, or by
The laser beam after phase modulation is passed through a phase modulator, and the phase modulation is canceled out by performing phase modulation with an opposite phase to the phase modulation, so that the wavelength chirping becomes zero or moves in the opposite direction. It is possible to improve optical transmission characteristics by

[Brief explanation of drawings]

1 to 3 are block diagrams of essential parts of a semiconductor light emitting device for explaining the principle of the present invention, FIG. 4 is a cutaway side view of essential parts of an embodiment of the present invention, and FIG. 5 is a DFB type semiconductor laser. 6 is a cross-sectional side view of essential parts for explaining a semiconductor light emitting device that integrates a semiconductor light emitting device and a semiconductor modulator; FIG. 6 is a line diagram for explaining the state of modulation in the semiconductor light emitting device shown in FIG. Similarly, FIG. 7 shows diagrams for explaining the occurrence of wavelength chirping. In the figure, l is an n-type 1nP substrate, 2 is a diffraction grating, 3 is a GarnAsP waveguide layer, 4 is an InP etch stop layer,
5 is a GalnAsP active layer, 6 is a GalnAsP light absorption layer, 6' is a GalnAsP phase modulation layer, 7 is an InP cladding layer, 8 is a high resistance isolation region, 9 is a p1 type Qa)nAs
P key+-/bu layer, 10A and IOB are p {! 1.11
electrode, 11 is the n-side electrode, 12 is the non-reflective coating film made of SiN, 3A is the electrode of the semiconductor laser part LD,
13B is an electrode of the light absorption layer type modulator part MD-EA, 13
C is an electrode of the phase modulator part MD-P, 14 is a drive power source, l5 is a light absorption type modulation power source, 16 is a phase modulation power source,
LD is a semiconductor laser part, MD-EA is a light absorption modulator part, MD-P is a phase modulator part, PSl is a drive power supply, PS2 is a light absorption modulation power supply, and PS3 is a phase modulation power supply. ing.

Claims (2)

[Claims] (1) A semiconductor laser has an active layer for generating laser light and an electrode for passing a driving current, and a light absorption layer that is connected to the active layer so that the laser light can be incident thereon. and a light absorption modulator portion having an electrode for applying a modulation voltage for light absorption modulation of the laser beam, and the laser subjected to the light absorption modulation and the phase modulation accompanying the light absorption modulation. A phase modulator, which has a phase modulation layer connected to the light absorption layer so that light can be incident thereon, and an electrode through which a modulation current flows for phase modulation in an opposite phase to the phase modulation that the laser beam is receiving. 1. A semiconductor light emitting device characterized in that a light emitting device and a light emitting device are integrated on the same substrate. (2) A semiconductor laser portion having an active layer for generating laser light and an electrode for passing a drive current, and a phase modulation layer continuous to the active layer so that the laser light can be incident. and a phase modulator portion having an electrode for applying a modulation voltage to perform phase modulation in an opposite phase to the phase modulation that would be received when the laser light is optically absorbed modulated; a light absorption type modulator part having a light absorption layer connected to the phase modulation layer so that the laser light can be incident thereon, and an electrode through which a modulation current flows for light absorption modulation of the laser light; 1. A semiconductor light emitting device characterized in that: and are integrated on the same substrate.